As one of the hot research fields in the area of panel displays at present, organic light emitting diode (OLED) displays, compared with liquid crystal displays (LCDs), have advantages such as low energy consumption, low production costs, self-illumination, wide viewing angles, high response speeds and the like, so that at present they are taking the place of conventional LCDs in tablet display devices such as mobile phones, PDAs, digital cameras or the like.
Because the present OLED displays have a large number of thin film transistors in their pixel circuits, how to reduce the ratio of the foot area of the capacitor(s) in a pixel unit to the total foot area of the pixel circuit has drawn a great attention to manufacturers.